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The mechanism, catalytic effect and solvent effect of the hetero-Diels-Alder reac- tions between 3-pyridinedithioesters and 1-phenylsulfanylbutadiene have been studied theoretically using density functional theory (DFT) at the B3LYP/6-31G(d) level. The results show that all of these reactions proceed in a concerted but asynchronous way. In some reactions the formation of C-S bond is prior to that of C-C bond and the opposite results are found in other reactions. The BF3 catalyst may lower the activation barriers by changing the energies of LUMO for 3-pyridine- dithioester. THF solvent has trivial influence on the potential energy surface of these reactions. With the BF3-catalyzed reactions, regioselectivity and stereoselectivity observed experimentally were predicted correctly by calculations and these results originate probably from C-H···F interaction in two transition states.
The mechanism, catalytic effect and solvent effect of the hetero-Diels-Alder reac- tions between 3-pyridinedithioesters and 1-phenylsulfanylbutadiene have been studied theoretically using density functional theory (DFT) at the B3LYP / 6-31G (d) level. The results show that all of these reactions proceed in a concerted but asynchronous way. In some reactions the formation of CS bond is prior to that of CC bond and the opposite results are found in other reactions. The BF3 catalyst may lower the activation barriers by changing the energies of LUMO for 3-pyridine-dithioester. With the BF3-catalyzed reactions, regioselectivity and stereoselectivity observed experimentally were predicted correctly by calculations and these results originate probably from CH · ·· F interaction in two transition states.